A frequently used optical fiber connector for terminating and connecting two optical fibers is one which is referred to as an ST.RTM. connector--ST being a registered trademark of AT&T. The design of an ST connector is disclosed in U.S. Pat. No. 4,934,785 and includes an assembly comprising a ferrule and a barrel for holding same. The ferrule (sometimes also referred to as a plug) has a narrow passageway through its center for receiving an end portion of an optical fiber whose protective coating has been removed. The barrel (sometimes also referred to as a base member) also includes a passageway for receiving the coated optical fiber, and it terminates in a cylindrical cavity which holds the ferrule. Interconnection with another optical fiber generally involves butting ferrules together in such a way that there is maximum coupling of the light rays between their included fibers. This is no easy task, particularly in single mode transmission where light rays are generally confined to a small region (mode field diameter) at the center of the fiber having a diameter which is less than ten microns. The ferrules, and hence the fibers themselves, are spring loaded so that they are urged together via a predetermined force. However, should the ferrules become slightly misaligned by the application of a non axial force, there will be a considerable forward loss in the amount of light coupled between fibers. Moreover, even an axial force applied to the cable will cause considerable forward loss in coupled light when it exceeds the compression force of the spring which urges the ferrules together. With an air gap, a significant increase also occurs in return loss, or reflectance, which is caused by a difference in refractive index created by any separation between optical fiber ends. The challenge, then, is to design a connector that eliminates, or at least minimizes, the effect of such forces.
An improvement on the above patent is shown in U.S. Pat. No. 4,812,009 which discloses an optical fiber con hector that includes an extender for transferring bending forces applied to its associated cable. Without the extender, these forces might cause the ferrule to move in such a way that optical disconnection occurs. During assembly of the connector, a ferrule/barrel assembly is captured between adjacent interior cavities of the cap using a C-shaped retainer which installs around the barrel after it is inserted through the free end of the cap. Thereafter, the extender is threaded onto the cable-insertion end of the cap. Unfortunately, threading the extender onto the cap is a process that can be performed incorrectly, and there are costs associated with each additional part and manual assembly.
Another problem associated with the above-described connector is its potential for optical disconnection. Recall that the ferrule/barrel assembly is biased outwardly of the cap by a compression spring, and that axial forces applied to the fiber optic cable are directly transferred to the ferrule/barrel assembly. Once the axial force exceeds the compression force of the spring (about 2 lbs.), there is optical disconnection.
U.S. Pat. No. 5,096,276 discloses a connector which attaches tensile strength members (aramid fibers) within the fiber optic cable to the connector housing rather than the ferrule/barrel assembly in order to protect against inadvertent optical disconnection. However, a relatively large number of precision parts are required. On the other hand, U.S. Pat. No. 5,142,601 discloses a connector that includes a single-piece holder which is split along its longitudinal axis so that a nylon-coated fiber can be installed by "after-attachment." Although the number of component parts is a reduction over known optical connecting devices, it is achieved with reduced functionality. For example, the ferrule and associated base member which holds it appear to be only loosely coupled to the holder via tension on the optical fiber itself. Such tension varies according to the skill of the manual assembler of the connector.
What is needed, and what is not supplied by the prior art, is an optical connector which protects against inadvertent disconnection caused by axial forces applied to the cable and which uses relatively few parts.